Bacteria are extremely small living things. While we measure our own sizes in inches or centimeters, {{U}}(72) {{/U}} . One micron is a thousandth of a millimeter; a pinhead is about a millimeter across. Red-shaped bacteria are usually from two to four microns long, while rounded ones are generally one microns in diameter. Thus, if you enlarged a rounded bacterium a thousand times, {{U}}(73) {{/U}} . An adult human magnified by the same amount would be over a mile (1.6 kilometers) tall.
Even with an ordinary microscope, you must look closely to see bacteria. {{U}}(74) {{/U}} , one finds that bacteria are barely visible as tiny rods or dots. One cannot make out any things of their structure. Using special strains, {{U}}(75) {{/U}} . Others have only one flagellum. The flagella (游丝) rotate, pushing the bacteria through the water. Many bacteria lock flagella and cannot move about by their own power, {{U}}(76) {{/U}}.
From the bacterial point of view, the world is a very different place from what it is to humans. To a bacterium, {{U}}(77) {{/U}} . Bacteria are so small that they are influenced by the movements of the chemical molecules around them. Bacteria under the microscope, even those with no flagella, often bounce about in the water. This is because {{U}}(78) {{/U}} . Molecules move so rapidly that within a tenth of a second the molecules around a bacterium have all been replaced by new ones; even bacteria without flagella are thus constantly exposed to a changing environment.
Sentence:
A. Using a magnification of 100 times.
B. It would be just about the size of a pinhead.
C. Water is as thick as molasses is to us.
D. The bacteria content different liquids.
E. Bacterial size is measured in microns.
F. While other can glide along over surfaces.
G. They collide with the water molecules and are pushed this way and that.
H. One can see that some bacteria have attached to the wavy-looking "hairs" called flagella.